Removing duplicate lines with uniq

To remove duplicate lines from a file use the command:

uniq in_file out_file

uniq searches the in_file
for consecutive duplicate
lines - a line that is immediately followed by one or more
lines that are identical to it - and removes them. The
result is an out_file that contains no duplicate lines.

Use the sort
command if you want to remove duplicate
lines that occur in different parts of a file.